Camshaft apparatus

ABSTRACT

Among a plurality of bearings that rotatably support a camshaft ( 1 ), the bearing closest to a pulley (P) is a rolling bearing ( 4 ), and the other bearings are plain bearings ( 3 ). The rolling bearing ( 4 ) is formed of a roller bearing portion ( 5 ) that has a first outer ring raceway surface ( 51 ) and a plurality of cylindrical rollers ( 53 ) that roll on the first outer ring raceway surface ( 51 ) and a ball bearing portion ( 6 ) that is arranged next to the roller bearing portion ( 5 ) in an axial direction and that has a second outer ring raceway surface ( 61 ) and a plurality of balls ( 63 ) that roll on the second outer ring raceway surface ( 61 ). The first outer ring raceway surface ( 51 ) and the second outer ring raceway surface ( 61 ) are formed on the inner peripheral surface ( 7 a) of a single outer ring ( 7 ).

TECHNICAL FIELD

The invention relates to a camshaft apparatus that is driven forrotation in synchronization with the rotation of an engine.

BACKGROUND ART

An existing camshaft apparatus used in an engine for an automobilerotatably supports a camshaft having a plurality of cams for actuatingintake and exhaust valves via a plurality of bearings (for example, seePatent Document 1). As shown in FIG. 3, in the support structure, allthe bearings are plain bearings 41, and the plain bearings 41 are usedto respectively support portions between the cams 43 of the camshaft 42.

The existing camshaft apparatus that uses the plain bearings for all thebearings has a large friction resistance because the plain bearings areused, so there is a problem that the running torque of the camshaftincreases and the fuel economy performance of the engine decreases. Inorder to solve the above problem, there is proposed that rollingbearings are used for all the bearings (for example, see Patent Document2),

RELATED ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Publication No. 8-218817

Patent Document 2: Japanese Patent Application Publication No.2006-226183

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the camshaft apparatus in which all the bearings that support thecamshaft are rolling bearings, when coaxiality is low at the time ofassembling the rolling bearings to an engine-side cylinder head, or thelike, the camshaft cannot smoothly rotate, so it is necessary to set thecoaxiality among the rolling bearings so as to be high. Therefore, it isnecessary to increase the machining accuracy of assembled portions ofthe cylinder head, or the like, so there is a problem that it isdifficult to manufacture the assembled portions. One of objects of theinvention is contemplated in light of the above situation, and is toprovide a camshaft apparatus that is able to reduce the running torqueof the camshaft and that is able to easily manufacture the assembledportions to which the bearings that support the camshaft are assembled.

Means for Solving the Problems

A camshaft apparatus according to one aspect of the invention includes:a camshaft having a plurality of cams in an axial direction and one endto which a pulley is connected; and a plurality of bearings thatrotatably support the camshaft on a housing, wherein, among theplurality of bearings, the bearing closest to the pulley is formed of arolling bearing, and the other bearing is formed of a plain bearing, therolling bearing includes: a roller bearing portion that has a firstouter ring raceway surface and a plurality of rollers that roll on thefirst outer ring raceway surface; and a ball bearing portion that isarranged next to the roller bearing portion in the axial direction andthat has a second outer ring raceway surface and a plurality of ballsthat roll on the second outer ring raceway surface, and the first outerring raceway surface and the second outer ring raceway surface areformed on an inner periphery of a single outer ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional view that shows a camshaft apparatusaccording to an embodiment of the invention.

FIG. 2 is an enlarged sectional view that shows a relevant portion ofFIG. 1.

FIG. 3 is a sectional view that shows an existing camshaft apparatus.

EMBODIMENTS OF THE INVENTION

Hereinafter, an embodiment of the invention will be described withreference to the accompanying drawings. FIG. 1 is a partially sectionalview that shows a camshaft apparatus according to the embodiment of theinvention. The camshaft apparatus C is to actuate the intake and exhaustvalves of an automobile engine, and is assembled to a housing H(cylinder head) formed of an aluminum block. The camshaft apparatus Cincludes a camshaft 1 having a plurality of cams 2, a plurality of (fourin the present embodiment) plain bearings 3 that rotatably support thecamshaft 1 and a single rolling bearing 4.

The camshaft 1 has a linear shaft body 11, a shaft member 12 connectedto one end (right side in FIG. 1) of the shaft body 11 and the pluralityof substantially egg-shaped cams 2 that are fitted around the outerperiphery of the shaft body 11. The shaft member 12 has an outsidediameter that is set to, for example, 18 to 20 mm, and is fixedlypress-fitted to one end of the shaft body 11 concentrically. A pulley Pfor rotating the camshaft 1 is connected to an end of the shaft member12 via a pulley mounting portion 13. Then, the pulley P is coupled to acrankshaft (not shown) that serves as an output shaft via a belt (notshown), and rotates in synchronization with the crankshaft. Power istransmitted to the camshaft 1 via the pulley P.

The cams 2 are arranged in units of pair at predetermined intervalsalong the axial direction of the shaft body 11. A through hole 2 a forpress-fitting the cam 2 to the outer peripheral surface 11 a of theshaft body 11 is formed in each cam 2.

Each plain bearing 3 is arranged between a corresponding one of pairs ofthe cams 2, and rotatably supports the shaft body 11. Each plain bearing3 is formed in a cylindrical shape, and its outer peripheral surface 3 ais fixedly fitted to an accommodating chamber inner surface of a housingH. In addition, the outer peripheral surface 11 a of the shaft body 11is in sliding contact with the inner peripheral surface 3 b of eachplain bearing 3 via an oil film.

The rolling bearing 4 is a bearing closest to the pulley P, androtatably supports the shaft member 12 of the camshaft 1. FIG. 2 is anenlarged view of a relevant portion of FIG. 1, showing the rollingbearing 4. The rolling bearing 4 has a single outer ring 7, and isformed such that a roller bearing portion 5 and a ball bearing portion 6are separated in the axial direction. The outer ring 7 is formed of, forexample, a bearing steel, a stainless alloy, or the like, in acylindrical shape, and its outer peripheral surface 7 a is fixedlyfitted to the accommodating chamber inner surface of the housing H.

The roller bearing portion 5 includes a first outer ring raceway surface51 formed on the outer ring 7, a first inner ring raceway surface 52formed on the shaft member 12, a plurality of cylindrical rollers 53rollably arranged between the first outer ring raceway surface 51 andthe first inner ring raceway surface 52 and a first cage 54 that retainsthe cylindrical rollers 53 at predetermined intervals along thecircumferential direction to thereby form a cylindrical roller bearing.

The first outer ring raceway surface 51 is integrally formed with a step7 c formed at one end side (left side in FIG. 2) from substantially thecenter portion of the inner peripheral surface 7 b of the outer ring 7.The first inner ring raceway surface 52 is integrally formed with theouter peripheral surface 12 a of the shaft member 12. The outerperipheral surface 12 a faces the first outer ring raceway surface 51.The cylindrical rollers 53 are, for example, formed of a bearing steel,a stainless alloy, or the like. Displacement of the cylindrical rollers53 toward one side (right side in FIG. 2) in the axial direction isrestricted by the step 7 c. The first cage 54 has a pair of annularportions 54 a that are arranged so as to be spaced apart in the axialdirection and a plurality of pillar portions 54 b that couple the pairof annular portions 54 a. A plurality of pockets 54 c are formed in thecircumferential direction by the space between any adjacent pillarportions 54 b and the pair of annular portions 54 a. Each cylindricalroller 53 is arranged in the corresponding pocket 54 c, and thecylindrical rollers 53 are retained at predetermined intervals along thecircumferential direction.

The ball bearing portion 6 is arranged next to the roller bearingportion 5 on the side adjacent to the shaft body 11 in the axialdirection. In addition, the ball bearing portion 6 includes a secondouter ring raceway surface 61 formed on the outer ring 7, a second innerring raceway surface 62 formed on the shaft member 12, a plurality ofballs 63 rollably arranged between the second outer ring raceway surface61 and the second inner ring raceway surface 62 and a second cage 64that retains the balls 63 at predetermined intervals along thecircumferential direction to thereby form a deep groove ball bearing.

The second outer ring raceway surface 61 is formed in a circular arcshape in cross section at the other end (right side in FIG. 2) fromsubstantially the center portion of the inner peripheral surface 7 b ofthe outer ring 7. The second inner ring raceway surface 62 is formed ina circular arc in cross section on the outer peripheral surface 12 a ofthe shaft member 12. The outer peripheral surface 12 a faces the secondouter ring raceway surface 61. The balls 63 are, for example, formed ofa bearing steel, a stainless alloy, or the like. The second cage 64 is asnap cage that is molded by resin, and a plurality of pockets 64 b foraccommodating the balls 63 are formed in the circumferential directionby a plurality of pillar portions 64 a that extend in the axialdirection.

Incidentally, particularly, a portion adjacent to the pulley P to whichpower is transmitted within the camshaft 1 receives a large load appliedbecause of belt tension. The applied loading occupies about 70% of theentire applied loading that acts on the whole of the camshaft 1.Therefore, in the rolling bearing 4, the roller bearing portion 5 thathas a loading capacity of about three times as large as that of the ballbearing portion 6 is arranged close to the pulley P. By so doing, aportion having a large applied loading within the camshaft 1 may bestably supported by the roller bearing portion 5 having a large loadingcapacity. In addition, displacement of the camshaft 1 toward both sidesin the axial direction is restricted by the ball bearing portion 6.

The rolling bearing 4 further includes seal members 8 and 9 forhermetically sealing the gaps between the outer ring 7 and the shaftmember 12. The seal members 8 and 9 are mainly formed of an elasticbody, such as synthetic rubber, and are respectively fitted to bothaxial ends of the inner peripheral surface 7 b of the outer ring 7.Grease (not shown) is filled in the space S that is hermetically sealedby the seal members 8 and 9. By so doing, it is possible to reliablylubricate the roller bearing portion 5 and the ball bearing portion 6 bythe grease filled in the space S while preventing foreign matter, suchas carbon sludge and metal powder, contained in lubricating oil of anengine from entering the space S. In addition, it is possible to reducenoise generated from the roller bearing portion 5 and the ball bearingportion 6 by the grease filled in the space S.

With the thus configured camshaft apparatus C according to the presentembodiment, the bearing closest to the pulley P is the rolling bearing 4among the plurality of bearings that support the camshaft 1, so themaximum applied load that acts via the pulley P within the camshaft 1may be supported by the rolling bearing 4 having a small frictionresistance. Thus, it is possible to effectively reduce the runningtorque of the camshaft 1. In addition, the other bearings that supportthe camshaft 1 are the plain bearings 3, so, in comparison with the casewhere all are rolling bearings as in the case of the existing art, it ispossible to set the coaxiality among the bearings so as to be low. Thisis because, when the plain bearings 3 are used as bearings that supportthe camshaft 1, a slight gap is formed between the outer peripheralsurface 3 a of each plain bearing 3 and the housing H, so, even when thecoaxiality among the bearings is decreased, the camshaft 1 may berotated without any trouble. As a result, it is not necessary toincrease the machining accuracy of the assembled portions (housing H) towhich the bearings that support the camshaft 1 are assembled, so it ispossible to easily manufacture the assembled portions. In addition, therolling bearing 4 is provided for the shaft member 12 at the end of thecamshaft 1, so the rolling bearing 4 may be applied to a camshaft thatis cast integrally from the cams 2 and the shaft body 11 other than theassembly-type camshaft 1 in which the cams 2 are externally fittedaround the shaft body 11.

Furthermore, the rolling bearing 4 has the roller bearing portion 5 andthe ball bearing portion 6, so the loading capacity may be increased bythe roller bearing portion 5, and displacement of the camshaft 1 in theaxial direction may be restricted by the ball bearing portion 6.Therefore, it is possible to suppress a decrease in the operatingperformance of the camshaft apparatus C due to the above applied load.In addition, the first outer ring raceway surface 51 of the rollerbearing portion 5 and the second outer ring raceway surface 61 of theball bearing portion 6 are formed of the inner peripheral surface 7 b ofthe single outer ring 7, so the number of components may be reduced, andmanufacturing cost may be reduced.

In addition, the first inner ring raceway surface 52 on which thecylindrical rollers 53 of the roller bearing portion 5 roll and thesecond inner ring raceway surface 62 on which the balls 63 of the ballbearing portion 6 roll are formed on the outer peripheral surface 12 aof the shaft member 12 of the camshaft 1, so the camshaft 1 may be usedas both the inner rings of the roller bearing portion 5 and ball bearingportion 6. Thus, the number of components may be reduced, andmanufacturing cost may be further reduced. In addition, the first andsecond inner ring raceway surfaces 52 and 53 may be formed on the shaftmember 12 before the shaft member 12 is connected to the shaft body 11,so machining the inner ring raceway surfaces 52 and 53 is easy.

The invention is not limited to the above described embodiment, but itmay be modified in design where appropriate. For example, in the aboveembodiment, the camshaft 1 is formed such that the shaft body 11 isseparately formed from the cams 2; instead, as described above, thecamshaft 1 may be integrally formed by casting from the shaft body 11and the cams 2. In addition, the roller bearing portion 5 may be formedas a needle bearing other than a cylindrical roller bearing.Furthermore, the ball bearing portion 6 may be formed as an angularcontact ball bearing when mounting space may be ensured, other than adeep groove ball bearing. In addition, the inner ring raceway surface 52of the roller bearing portion 5 and the inner ring raceway surface 62 ofthe ball bearing portion 6 are formed on the outer peripheral surface 12a of the shaft member 12; instead, the inner ring raceway surface 52 ofthe roller bearing portion 5 and the inner ring raceway surface 62 ofthe ball bearing portion 6 may be formed on the outer peripheral surfaceof an inner ring separately mounted on the shaft member 12.

DESCRIPTION OF REFERENCE NUMERALS

-   1 camshaft-   2 cam-   3 plain bearing (bearing)-   4 rolling bearing (bearing)-   5 roller bearing portion-   6 ball bearing portion-   7 outer ring-   11 shaft body-   12 shaft member-   51 first outer ring raceway surface-   52 first inner ring raceway surface-   53 cylindrical roller (roller)-   61 second outer ring raceway surface-   62 second inner ring raceway surface-   63 ball-   C camshaft apparatus-   H housing-   P pulley

1. A camshaft apparatus that includes: a camshaft having a plurality ofcams at predetermined intervals along an axial direction and one end towhich a pulley is connected; and a plurality of bearings that rotatablysupport the camshaft on a housing, characterized in that: the bearingclosest to, the pulley among the plurality of bearings is formed of arolling bearing, and the other bearing is formed of a plain bearing, therolling bearing includes: a roller bearing portion that has a firstouter ring raceway surface and a plurality of rollers that roll on thefirst outer ring raceway surface; and a ball bearing portion that isarranged next to the roller bearing portion in the axial direction andthat has a second outer ring raceway surface and a plurality of ballsthat roll on the second outer ring raceway surface, and the first outerring raceway surface and the second outer ring raceway surface areformed on an inner periphery of a single outer ring.
 2. The camshaftapparatus according to claim 1, wherein a first inner ring racewaysurface on which the rollers of the roller bearing portion roll and asecond inner ring raceway surface on which the balls of the ball bearingportion roll are formed on an outer peripheral surface of the camshaft.3. The camshaft apparatus according to claim 2, wherein the camshaftincludes a shaft body and a shaft member that is concentricallyconnected to one end of the shaft body and to which the pulley isconnected, and the first inner ring raceway surface and the second innerring raceway surface are formed on an outer peripheral surface of theshaft member.